1. Field of the Invention
The present invention relates to a transmission for a vehicle.
2. Description of Related Art
As an example, WO2006/009014 discloses a method of controlling an electronically-controlled belt continuously variable transmission (“ECVT”) as described below.
A target change-gear ratio is determined by a throttle opening signal and a vehicle speed signal. A target sheave position of a movable sheave half of a primary sheave is calculated from the determined target change-gear ratio. Then, a voltage such that the movable sheave half of the primary sheave is displaced to the calculated target sheave position is applied to an electric motor for driving the movable sheave half of the primary sheave. Thereby, the change-gear ratio is controlled to reach the target change-gear ratio.
However, a problem occurs in the method of controlling the change-gear ratio of WO2006/009014. As a centrifugal clutch disposed between an output shaft of the ECVT and the drive wheel wears out with time, engine speed increases during low-speed operation. This problem of increased engine speed occurs particularly during idling.